1. Field of the Invention
The present invention relates to an image processing method, an apparatus and a memory medium therefor.
2. Related Background Art
For adjusting the color balance of a photographic image there are conventionally known two methods, namely:
(1) matching the color balance before picture taking; and
(2) correcting the image after picture taking.
As an example of the method (1), there is known an color balance adjusting method utilizing a white balance switch for example of a video camera. In this method, the white color balance of the taken image is adjusted by preliminarily taking white paper or the like before starting the main picture taking operation.
The method (2) is widely exercised for example in the printing field, but depends on the experience and intuition of experts.
On the other hand, with the recent spreading of digital cameras and photo scanners, the digitization of the photographic image can be easily achieved by the general users. Also the output equipment represented by ink jet printer is progressing toward higher image quality and lower cost, that the general users can easily print the photograph at home.
However, in case of printing a digitized photographic image, the quality of the outputted image is still insufficient.
For example, for printing the RGB signals from an input equipment by an output equipment represented by an ink jet printer through so-called personal computer or the like, there has been tried color matching between the input equipment and the output equipment thorough the CIE XYZ color space by Color Think (trade name) in the Apple McIntosh or by CMS in the Microsoft Windows (trade name). It is however very difficult to execute these adjustments in strict manner, because the color reproduction range is naturally different between the input equipment and the output equipment, and there is also involved a basic difference in the working principle that the input equipment works on the R, G and B light emissions while the output equipment works on the C, M, Y and K reflective colors.
Even if the color matching is achieved between the input equipment and the output equipment by overcoming such difficulties, the image satisfactory for the user cannot be obtained merely by strictly reproducing the image from the input equipment as a print if such original image from the input equipment is not satisfactory. Such situation arises in case of an overexposure or an underexposure in the image taking or a distorted color balance of the entire image caused by a “color fog” phenomenon.
For example, in case of auto picture taking by a camera with the AE (automatic exposure) function, there results a generally dark image of so-called underexposure state if the background of the object is principally constituted by blue sky, but there results an overexposure state if the background is principally dark, so that the intended object is not always recorded in a best state.
Also in case of a digital camera, the image is picked up by a CCD, so that a wavelength region not sensitive to the human eye is also contained in the image signal. If such signal is processed as a part of the RGB signals, the original invisible color becomes visible to distort the color balance. Naturally there is incorporated an infrared cut-off filtering but such filtering is not necessarily complete, and the color balance cannot be completely corrected within the limitation of real-time processing. As a result there is caused a “color fog” phenomenon, distorting the color balance of the entire image.
Since similar phenomena may occur in the photo scanner or the flat bed scanner, the color balance may be distorted in the digitization with such scanner even if the original negative or reversal film is in the optimum state.
Therefore, in order to obtain satisfactory output result it is necessary to correct the input image data themselves into the image data of appropriate exposure with satisfactory color balance, and, for this purpose, there is required a simple method not requiring cumbersome operations by the user, with a sufficiently acceptable processing speed.